This invention relates to a method for the determination of dopamine -.beta.- hydroxylase, hereinafter referred to as D.beta.H. More particularly, this invention relates to a method for the determination of D.beta.H activity in biological fluids with an oxygen-sensing electrode which measures dissolved oxygen in solution.
D.beta.H is an enzyme which catalyzes the oxidation of dopamine to norepinephrine according to the following equation: ##STR1## Dopamine, which is one of the biogenic amines, has been shown to play an important role in the sympathetic motor system. A diminished supply of dopamine in the corpus striatum of the brain is associated with Parkinson's disease. The enzyme D.beta.H, which oxidizes the catecholamine dopamine to norepinephrine, is apparently released from the sympathetic nerves together with the catecholamines. An elevated level of D.beta.H has been associated with hypertension and it has been proposed that plasma D.beta.H activity may serve as an index of the activity of the sympathetic nervous system, Schanberg et al, Science 183, 523-4 (1974). Consequently, methods for the determination of D.beta.H are of significant clinical interest.
Presently available methods for the determination of D.beta.H in biological fluids include a fluorometric method which employs dopamine as the substrate, Von Euler et al, Acta Physiol. Scand. 33, 45 (1955); an enzyme conversion method employing tyramine-.sup.3 H as the substrate based on the conversion of tyramine to octopamine and oxidation of the latter compound with periodate, Pisano et al, Biochim.Biophys. Acta 43, 566 (1960); a non-isotopic method employing similar such conversion of tyramine, Kuzuya and Nagatsu, Enzymologia 36, 31 (1969); and a photometric procedure involving the photometric assay of p-hydroxybenzaldehyde following the previously described oxidation of the octopamine with periodate, Nagatsu and Udenfriend, Clin. Chem. 18, 980-83 (1972).
Although the foregoing assay procedures are useful and sensitive, they involve numerous steps and are time consuming.